Summary Of Significant Accounting Policies (Schedule Of Excise Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Line Items]
Excise tax expense	$ 282	$ 265	$ 259
Union Electric Company
Accounting Policies [Line Items]
Excise tax expense	164	153	151
Ameren Illinois Company
Accounting Policies [Line Items]
Excise tax expense	$ 118	$ 112	$ 108